With active volcanoes as close as 80 miles of Anchorage city limits, Alaskans are grateful for the professional volcano watchers who work in a nondescript building on the campus of Alaska Pacific University, topped with a massive array of tracking and communication instruments. “The August 18, 1992 Spurr eruption, sent an ash cloud here that coated every flat surface,” remembers geologist Game McGimsey of the Alaska Volcano Observatory.

“You could feel it falling on your hair. The second day was actually worse, the air quality at rush hour was terrible, with all the ash getting stirred up by traffic and jet engines at the airport. It was like being in a dust storm, with all the ash suspended in the air.”

Thanks to AVO, city residents have an early warning system on such volcanic events and officials can direct at-risk people to stay inside, businesses to cover computers and airports to close. The Observatory keeps tabs on the four Cook Inlet volcanoes nearest Anchorage and others throughout the state, providing hazard reports and eruption notifications to federal, state and municipal agencies.

Says McGimsey, “We base our forecasts of potential explosions on each volcano’s previous eruptive activity and the recorded seismicity, such as the previous deposits of flows and ash and ground rumblings observed from our instrumentation. It’s not as precise as say, a hurricane warning, but we can usually give some advance notice.”

In addition to the abundant monitoring instrumentation on the cones [link to monitoring blog post], AVO’s forecasting requires volcanologists like McGimsey to get into the field regularly. “It’s the nature of the job. We keep ourselves in good physical condition. We’re required to have aviation safety training, and first aid and CPR certifications. Some of us have climbing skills. When we go out we take enough emergency equipment to survive the night, things like extra clothes, first aid, food, water, and in bear country a firearm or bear spray.” McGimsey notes that with this gear, on top of a frontier scientist’s standard tools–rock hammer, GPS, camera, sample bags, notebooks, ash measurement equipment, spatulas, surveyor’s equipment, radio and a satellite phone—his backpack typically weighs 30 to 35 pounds.

McGimsey says AVO scientists closely monitor data on the Cook Inlet volcanoes and have good communication with field crews to reduce the potential of anyone being in harm’s way while conducting field studies and research. “We have a good understanding of their previous eruption style and character. The monitoring data give us an idea of when a volcano is restless and the nature of the activity. The seismicity usually ratchets up when lava is rising from depth to shallow levels beneath a volcano, and any deformations of the volcano surface indicating rising magma are tracked by GPS (global positioning system). We evaluate this information against what the volcano has done in the past hundred to few thousand years. From that we anticipate the nature and magnitude of the new activity.”

In 1992, for example, AVO scientists were able to watch a gradual escalation in seismic activity at Spurr over a ten-month period, giving the public advance notice of the unrest, and eventually a warning that an eruption could be days or weeks away. It turned out to be days.

Recalling the 1992 Spurr eruption, McGimsey notes the ash was inescapable. “People would turn on interior car air fans and ash would blow in. It accumulated on rooftops and filled up rain gutters. Recently we got a call from a guy who was cleaning out his house who had saved a 100-pound bag of ash he had meticulously collected then, asking if we wanted it. We gladly accepted it since we get a lot of requests from school teachers and researchers who want samples.”

The ash volume generated from the August 18, 1992 eruption was estimated at 110 million cubic meters of ash, enough to fill over 14 million standard dump trucks carrying 10 cubic yards each, or 59 Anchorage Domes! It accumulated to three millimeters in Anchorage.

According to McGimsey, factors other than ash are also considered in volcano hazard assessments. “We base the power of eruptions on the VEI [volcanic explosivity index], which accounts for the volume of erupted products, eruption cloud height, duration of the eruption, and other factors. A mega-colossal event would be an 8 (Yellowstone, 640,000 BP). Pinatubo (1991) was a 6, Mount St. Helens (1980) was a 5, Mt. Spurr (1992) was a 4. Events that produce lots of lava but have non-explosive eruptions are low on the scale. So a small event on Redoubt or Mt. Spurr is typically higher on the scale than what you see in Hawaiian volcanoes that produce a lot more lava (Kiluaea, 1983-present, a VEI 1).”

So what should Alaskans expect from the Cook Inlet volcanoes including Redoubt, Augustine and Spurr? Does the prospect of a Mount St. Helens within viewing distance of a major city loom? McGimsey says, “In the short term, we expect our local volcanoes to behave as they have in the historical past. Mt. Spurr typically produces sustained explosive eruptions lasting a few hours that send up ash tens of thousands of feet. Augustine has produced lava domes and minor ash plumes in its last four to five eruptions. It has a history of summit flank collapse, about 12 times in last two thousand years—the last being in 1883–so it’s likely only a matter of time until the next collapse occurs.” Frontier scientists at the volcano observatory will be watching for it.